Recently, with a high energy concentration, secondary battery having a positive electrode such as a conductive polymer and a transition metal oxide and a negative electrode such as a lithium metal or a lithium alloy (hereinafter, briefly referred to as a lithium metal) has been proposed to replace a Ni—Cd battery and a lead battery. However, when charging and discharging are repeatedly performed, this secondary battery is subject to large reduction of capacity due to degradation of the positive electrode or the negative electrode, and thus there remains a practical problem. In particular, degradation of the negative electrode leads to generation a mossy lithium crystal called as a dendrite, and with repetitive charging and discharging the dendrite penetrates a separator to cause a short-circuit inside the battery, and in some cases, there might have a problem in terms of safety such as explosion of the battery.
Here, in order to solve the foregoing problems, a battery has been proposed having a negative electrode made of a carbon material such as graphite and a positive electrode made of a lithium containing metal oxide such as LiCoO2. This battery is a so-called rocking chair type battery such that, after assembling the battery, the lithium is supplied from the lithium containing metal oxide of the positive electrode to the negative electrode for charging and the lithium of the negative electrode is supplied backed to the positive electrode for discharging. This is distinguished from the lithium battery that uses metal lithium in that only the lithium ions are used in charging and discharging rather than using the metal lithium at the negative electrode, so that it is called as a lithium ion secondary battery. This battery has characteristics such as high voltage, high capacity, and high stability.
The lithium ion secondary battery is widely used for a mobile phone and a notebook personal computer, and thus there is a need for improvement of energy density. Generally, increases in each discharging capacity of the positive electrode and the negative electrode, improvement of charging and discharging efficiency, and improvement of electrode density are examined. In general, in designing a cell, a thickness and a density of each electrode is determined such that a charging amount of the positive electrode is identical to a charging amount of the negative electrode. Therefore, a discharging capacity of the cell is determined by a the lower efficiency between charging and discharging efficiencies of the positive electrode or the negative electrode, and thus a cell capacity grows larger as the charging and discharging efficiency is increased.
A research and development has been made on the negative electrode that uses an amorphous material such as tin oxide or polyacenic semiconductor (hereinafter, referred to as PAS) as a negative electrode for the lithium ion secondary battery. Examples of the PAS, which can be obtained through annealing aromatic polymer, includes insoluble and infusible base having a polyacene-based skeletal structure as disclosed in Japanese Examined Patent Application Publication Nos. Hei1-44212, and Hei3-24024. In addition, the PAS having a BET specific surface area of 600 m2/g can be obtained through a method disclosed in a method disclosed in Japanese Examined Patent Application Publication No. Hei3-24024. These amorphous materials have a high capacity, and a high nonreversible capacity. For this reason, with a typical arrangement of the typical lithium ion secondary cell, 100% of a negative electrode capacity can be used while only 60 to 80% of a positive electrode capacity can be used, which leads to not that high capacity.
With respect to this, the inventors herein achieved a high capacity by carrying the lithium ion to the negative PAS in advance, according to a method disclosed in Japanese Unexamined Patent Application Publication No. Hei8-7928. With the lithium ion to the negative PAS, 100% of discharging capacity for both the positive and negative electrodes can be used and thus a high capacity can be achieved, compared to a conventional design where only 60 to 80% of the positive electrode capacity can be used.
As described above, the lithium ion secondary battery has been studied as a high capacity and powerful power supply and commercialized as a primary power supply of typical notebook computer or mobile telephone. Of these, the mobile telephone has progressed into a small-sized and light-weighted one, and thus there is also a need for a small sized and light weighted lithium ion secondary ion used for the primary power supply. As a result, an outer case of a squared battery is changed from iron to aluminum and a weight is significantly reduced. In addition, there is a need for a thin battery having a thickness of 4 mm or 3 mm, so that a film battery that uses an aluminum laminated film as an outer material has been widely used with an increasing pace. In addition, while focusing on environmental issues, a storage system of a regenerative energy using a solar photovoltaic or a wind power plant, a distributed type power supply for the purpose of regulating a power load, or an automobile power supply (main power and auxiliary power) involved in a gasoline car have been progressively developed. In addition, up to now, while a lead battery is used for a power supply of electric equipment of the automobile, apparatuses such as a power window or a stereo has recently improved, and thus there is a need for a new power supply in terms of an energy density and an output density. At the same time, in terms of battery shape, there is also a need for an arrangement of a thin frame that uses a laminated film as an outer case, compared to the conventional rounded or squared type. This is less restrictive to location for a case where a space is limited such as a load conditioner installed in the household or a vehicle trunk, and thus, examination thereof is substantially progressed.
Like this, a film type lithium ion secondary battery has been widely used in various fields as a high capacity and space saving power supply.
As a method of carrying lithium ion to the negative electrode of the lithium ion secondary battery in advance, one cell having metal lithium in addition to the lithium ion secondary battery is arranged to carry a predetermined amount of lithium ion into the negative electrode, however, it is not desirable due to its complicated manufacturing process.
Regarding this, as an industrially convenient way, a method of electrochemically contacting the lithium metal and a negative electrode arranged in the cell is proposed. In a given method, carrying the lithium ion with electrochemical contact between the lithium metal and the negative electrode can be facilitated by using a material having an opening that penetrates a front and rear surfaces, such as expanded metal, as a positive electrode collector and a negative electrode collector. In addition, the lithium ion can be readily carried with the lithium metal arranged to face the negative or positive electrode.
However, in the method of electrochemically contacting the lithium metal and the negative electrode, carry is non-uniformly provided between the negative electrode arranged near the lithium metal and the negative electrode around far from the lithium metal, or even between a center and a corner in a sheet of the negative electrode. In addition, it is impossible to check whether a predetermined amount of lithium ion is carried, and thus a voltage of the electrical storage device is just used as a reference.
Further, in the method of electrochemically contacting the lithium metal with the negative electrode, while carry of the lithium ion is initiated at the time of injecting the electrolyte, the electrode is not well fixed at the time of injecting the electrolyte solution. Therefore, a problem occurs that the negative electrode is hardened in a rippled shape.
In particular, for a thin film type electrical storage device that uses an aluminum laminated film as an outer case material, a contact pressure from the outer container is weak so that the phenomenon appears noticeably, and the strain and wrinkle of electrode leads to cell shape-change. When the lithium ion is carried with the electrode in the rippled shape, it will be hardened as it is, thus leading to the distorted cell and thus degradation of the battery performance.
In addition, when carry of the lithium ion is initiated, the negative electrode emits a heat and thus a temperature increases. Here, when the temperature increases while the cell is not fully sealed, a problem such as solvent evaporation may occur. In particular, when more than two types of solvents are mixed, a composition of the solvents may vary, which causes non-uniform characteristics between cells.
Therefore, an object of the present invention is to provide an electrical storage device and a manufacturing method of an electrical storage device, with which the electrical storage device can be easily manufactured, it can be checked whether a predetermined amount of lithium ion is carried, the potential of a positive or negative electrode can be controlled at the time of charging and discharging, and non-uniform carry of the lithium ion and shape-change of the negative electrode can be readily prevented.